Poly lowers are pretty terrible. There is not enough material around the receiver extension/rear takedown pin for the type of material being used. When they fail, they fail here. The BCG cycling into the receiver extension stresses transfers forces to the portion between the receiver extension and the take down pin and they catastrophically fail.

There is no way to solve this as the design calls for a much higher tensile material in this area. The calvary arms lower seem to be the best in this regard as they added significantly more material/reshaped above the pistol grip around the take down pin/receiver extension necessitating integrating the stock/grip.

A polymer lower might be cool to mess around with in making a lightweight plinking toy but I wouldn't use it for anything serious or on a gun that will see any sort of high round count.

There is no way to solve this as the design calls for a much higher tensile material in this area. The calvary arms lower seem to be the best in this regard as they added significantly more material/reshaped above the pistol grip around the take down pin/receiver extension necessitating integrating the stock/grip.

A polymer lower might be cool to mess around with in making a lightweight plinking toy but I wouldn't use it for anything serious or on a gun that will see any sort of high round count.

I actually like the looks of this more than regular but 180 for a stripped lower +tax and dros Is way to Expensive

[QUOTE=DirtyLaundry;9547411]Poly lowers are pretty terrible. There is not enough material around the receiver extension/rear takedown pin for the type of material being used. When they fail, they fail here. The BCG cycling into the receiver extension stresses transfers forces to the portion between the receiver extension and the take down pin and they catastrophically fail.

I actually like the looks of this more than regular but 180 for a stripped lower +tax and dros Is way to Expensive

Yea, looks wise its love it or hate it but capabilities wise its about as light as you can get as far as lower/grip/stock goes and I would trust this design much more than a simple polymer copy of the aluminum part.

That said if you're looking to build an AR15 on the cheap I see no reason to look further than a cheap forged piece from someone like PSA. PSA lowers regularly go for $80 and there's a plethora of lowers form other vendors local and online for $100 or less, iirc turners even had an off-brand lower recently on sale for $55.

We're talking ounces difference in weight while being much more durable. These poly lowers are for people chasing every last ounce of weight away for either novelty or some sort of lightweight backpack gun. IMO if you're going to go that far I would go with a different platform entirely, the SU-16 comes to mind.

I took my delton upper today to the one in Chino Hills. The manager tried mounting my upper onto that lower and it wouldn't close. He struggled and looked puzzled and pissed. Then he got another lower, an aluminum one this time and snapped my upper easily onto it. He grunted and seemed pissed at the fact that he helped me and I let him realize that the ATI lower they have is garbage. I think he was embarrassed because other people were observing us as he tried to mount my upper but couldn't. He probably got mad at me for making that lower look like crap and possibly his store. I was polite and all too because he let me mount my upper first before deciding to buy it but after witnessing for myself that it wasn't working I just walked away :/

went to turners today Checked out the M&P Lower. That thing weighs Nothing. decided to buy it. Going to skip all the Polymer stuff for now. Maybe in the future ill build an ar made mostly of polymer. but for now i'll stick with aluminum for lightweight lowers.